In recent years, electronic devices or equipments such as LSI which are used in CPU or memories have been more and more enhanced in performance characteristics, leading to increase in operating frequency and reduction in size of the apparatuses. On the other hand, there occur various extensive problems such as increased transmission loss owing to the increase in operating frequency, and prolonged delay time owing to fineness of circuit wirings.
To solve these problems, it has been demanded to develop low-dielectric constant and low-dissipation factor insulating materials used in a multilayer wiring structure of electronic circuits. In order to reduce a dielectric constant of a layer insulation film, studies have been made to introduce voids into the film. However, when voids having non-uniform sizes are introduced into the film to reduce its dielectric constant, there tends to occur such a problem that the resulting film is deteriorated in strength thereof.
Patent Document 1 discloses a process for producing a ceramic film such as a mesoporous silica film having a dielectric constant of 2 to 3 in which a film-forming liquid containing a ceramic precursor, a catalyst, a surfactant and a solvent is prepared, and the thus prepared film-forming liquid is applied onto a substrate to remove the solvent therefrom.
Patent Document 2 discloses a low-dielectric constant film formed of a porous material of an organic group-containing silicon oxide wherein the silicon oxide contains silicon atoms at least a part of which form carbon-to-silicon bonds with two or more positions of organic groups, and the porous material is a mesoporous material having a peak pore diameter of 1 to 30 nm.
However, in the methods described in Patent Documents 1 and 2, a calcination step is required to remove a surfactant used for formation of the films. Therefore, there tend to arise the problems such as limitation to the kind of substrate used therein which will be disadvantageous from the viewpoint of a versatility of materials, etc.
Also, Patent Document 3 discloses a process for producing a low-dielectric constant insulating film in which a solution containing fine particles having a bond of a silicon atom and an oxygen atom and containing holes, a resin and a solvent is applied onto a substrate to form a thin coating film thereon, and then the thus coated substrate is heated.
In addition, Patent Document 4 discloses a low-dielectric resin composition containing hollow particles and a thermosetting resin in which silica particles having an average porosity of 30 to 80% by volume and an average particle size of 0.1 to 20 μm are used as the hollow particles to reduce a dielectric constant and a dissipation factor of the composition, and a prepreg prepared by impregnating a substrate with the low-dielectric resin composition and then heating and drying the thus impregnated substrate.
However, in the methods described in Patent Documents 3 and 4, the obtained films, etc., are still unsatisfactory in dielectric constant and dissipation factor.    Patent Document 1: JP 2001-226171A    Patent Document 2: JP 2003-86676A    Patent Document 3: JP 2005-167266A    Patent Document 4: JP 2008-031409A